Method and system for the support of a long drx in an LTE_ACTIVE state in a wireless network

Technical field of method and system for supporting long DRX in LTE_ACTIVE state in wireless network

[0001] The present disclosure generally relates to the Long Term Evolution (LTE) of the Third Generation Partnership Project (3GPP), and specifically relates to

Discontinuous reception (DRX) of user equipment (UE) in LTE infrastructure.

Background technique

[0002] In the long-term evolution infrastructure, the UE can be in one of two radio resource control (RRC) states.

These states are LTE_IDLE and LTE_ACTIVEo

[0003] The UE may be configured for discontinuous reception (DRX) in the LTE_IDLE and LTE_ACTIVE states. DRX allows the UE to synchronize its listening cycle with the known network paging cycle. By synchronizing the listening period, the UE can turn off its wireless transceiver during standby, thereby greatly saving battery resources. As those skilled in the art will understand, unless the UE is overused, a large amount of UE battery consumption comes from monitoring the paging channel and measuring the standby period of the serving cell and neighboring cells. The DRX parameter allows the mobile phone to synchronize with the network and know that it will not receive other signals until a certain time has passed.

[0004] In this UMTS system, the use of DRX in the IDLE state is used, and the DRX parameters are signaled to the UE through the network and the UE is synchronized with the network to use DRX in the IDLE state. As will be understood, in the IDLE mode, the UE The cell can be changed from one cell to another. Therefore, the use of DRX parameters will not cause significant problems.

[0005] However, in the ACTIVE state, there are various problems with turning off the receiver based on the DRX parameters. This includes the fact that only network-controlled handovers are allowed in the LTE_ACTIVE state. Similarly, other issues include: effective signaling for activation and deactivation of DRX, measurement needs of network signals during DRX, processing of missed handover opportunities, and processing of the length and reconfiguration of the DRX value that entities in the network can request for DRX activation The problem of DRX cycle.

Summary of the invention

[0006] The present disclosure may provide various methods and systems for solving the deficiencies of DRX in the LTE_ACTIVE state in the prior art.

[0007] Specifically, the DRX signaling process between the UE and the eNB is described, where the eNB signals the DRX value and timing margin as part of the modified MAC-PDU header. The DRX value signaled by the eNB may vary from zero indicating DRX deactivation to a value for the DRX cycle. The timing margin can indicate the delay of activating DRX to overcome NACK-ACK misinterpretation or ACK-NACK misinterpretation. In one embodiment, the timing margin may also be signaled by RRC.

[0008] In one embodiment, the DRX value may be incremented to a specific maximum value defined in the standard or signaled. If data has not been received for a predetermined number of DRX cycles, incrementing can be performed without being signaled by the UE and eNB. In another embodiment, the DRX value can be decremented until DRX is deactivated, without UE and eNB signaling.

[0009] In another embodiment, the traffic characteristics of the application layer can utilize DRX cycle optimization to improve battery life. In this case, the UE can send a request to initiate or modify the DRX value to the eNB, and the eNB can accept the value or reject the value. Various considerations including mobility, cell location, traffic characteristics, or missed handover opportunities can be determined for the UE and eNB to select and accept DRX values.

[0010] In another embodiment, if a certain threshold signal value is reached within a certain amount of time, by shortening the root

According to the measurement period of the DRX cycle, the measurement accuracy is improved. Therefore, in the case of signal degradation, the UE can determine that if the quality of the signal drops below the threshold within a predetermined time, it needs to perform more frequent measurements. Subsequently, if the signal rises above the threshold within a certain period of time, the measurement period can be increased, or a switching condition can be triggered if the signal falls below the threshold.

[0011] In another embodiment, if the channel quality or signal strength of the serving cell is judged to be less than the neighboring cell by a threshold within a certain duration, the missed handover opportunity can be processed. A procedure for switching to a target eNB is disclosed.

[0012] Therefore, the present disclosure provides a DRX signaling method between an evolved node B (eNB) and a user equipment (UE) in a long-term evolution infrastructure. The method includes the following steps: Provide the DRX value or the encoded DRX value in the header of the data unit; and activate, deactivate or reconfigure DRX based on the provided DRX value

[0013] The present disclosure also provides a method of supporting application layer traffic characteristics to improve the battery life of a user equipment (UE) communicating with an evolved node B (eNB), which includes the following steps: UE-based application traffic characteristics To request discontinuous reception (DRX) from the UE; to receive the request from the UE at the eNB; and to agree to the alternative period or reject the request at the eNB.

[0014] The present disclosure also provides a method for improving measurement accuracy during discontinuous reception (DRX) on a user equipment (UE). The method includes the following steps: checking the channel quality of the serving cell or Whether the signal strength is lower than the first threshold; and if so, shorten the measurement period to have a shorter measurement period than the DRX period.

[0015] The present disclosure also provides a method for handling missed handover opportunities based on discontinuous reception (DRX) in a user equipment (UE), the method includes the following steps: checking the channel of the serving cell in a specific time interval Whether the quality or signal strength is less than the channel quality or signal strength of the neighboring cell; and if so, connect to the neighboring cell.

[0016] The present disclosure also provides: an evolved node B (eNB) operating in a long-term evolution infrastructure, the eNB is characterized by relying on the following steps: providing in the header of the media access control protocol data unit (MAC-PDU) DRX value; and activating or deactivating DRXo based on the DRX value

[0017] The present disclosure also provides a user equipment (UE) operating in a long-term evolution (LTE) infrastructure. The UE is characterized by relying on the following steps: receiving a media access control protocol data unit (MAC-PDU) The DRX value in the header does not acknowledge the MAC-PDU; and the DRX is activated, deactivated or reconfigured based on the DRX value.

Description of the drawings

[0018] This application will be better understood with reference to the accompanying drawings, in which:

[0019] FIG. 1 is a block diagram showing a long-term evolution user plane protocol stack;

[0020] FIG. 2 is a block diagram showing a long-term evolution control plane protocol construction system;

[0021] FIG. 3a is a flowchart showing a method of activating, deactivating and reconfiguring the DRX cycle using the MAC-PDU header from the eNB side;

[0022] FIG. 3b is a flow chart showing a method for affirming the activation, deactivation or reconfiguration of the DRX cycle from the UE side;

[0023] FIG. 4a is a flowchart showing a method for the UE to support application traffic characteristics to improve the battery life of the UE;

[0024] FIG. 4b is a flowchart showing a method for UE to support application traffic characteristics to improve battery life on the eNB side;

[0025] FIG. 5 is a diagram showing a signal strength threshold and a measurement cycle time;

[0026] FIG. 6a is a flowchart showing the procedural steps involved in switching from the UE side to the target eNB;

[0027] FIG. 6b is a flowchart showing the procedural steps involved in switching from the eNB side to the target eNB;

[0028] FIG. 7 is a diagram showing a channel state without any uplink data, starting below a lower threshold and then above the threshold;

[0029] FIG. 8 is a diagram showing a channel state with uplink data, starting below a lower threshold and then above a higher threshold;

[0030] FIG. 9 is a diagram showing signal degradation that triggers a switching condition.

Detailed ways

[0031] Reference is now made to the drawings. Figure 1 is a block diagram showing a long-term evolution (LTE) user plane protocol stack.

[0032] The UE 110 communicates with an evolved node B (eNB) 120 and an access gateway (aGW) 130.

[0033] The various layers are shown in the protocol stack. Both the UE 110 and the aGW 130± show the Packet Data Convergence Protocol (PDCP) layer 140. The PDCP layer 140 performs Internet Protocol (IP) header compression and decompression, user data encryption, user data transmission, and maintenance of the serial number (SN) of the radio bearer.

[0034] Below the PDCP layer 140 is the radio link control protocol layer 142 that communicates with the radio link control protocol layer 142 on the eNB 120. As will be understood, communication occurs through the physical layer in the protocol stack as shown in FIGS. 1 and 2. However, the RLC layer 142 of the eNB 120± interprets the RLC-PDU from the RLC layer 142 of the UE.

[0035] Below the RLC layer 142 is a medium access control (MAC) data communication protocol layer 146. As those skilled in the art will understand, the RLC and MAC protocols form the data link sublayer of the LTE wireless interface and reside on the eNB and the user equipment in the LTE.

[0036] Layer 1 (L1) LTE (physical layer 148) is under RLC/MAC layers 144 and 146. This layer is the physical layer used for communication.

[0037] Referring to FIG. 2, FIG. 2 shows the LTE control plane protocol architecture. In FIG. 2, reference numerals similar to those used in FIG. 1 will be used. Specifically, UE 110 communicates with eNB 120 and aGW 130. In addition, the physical layer 148, the MAC layer 146, the RLC layer 142, and the PDCP layer 140 exist in FIG. 2.

[0038] FIG. 2 also shows a non-access stratum (NAS) layer 210. As will be understood, the NAS layer 210 can include mobility management and session management.

[0039] The Radio Resource Control Protocol (RRC) 220 is a part of the protocol stack and is responsible for the allocation, configuration and release of radio resources between the UE and E~UTRAN (Evolved Universal Terrestrial Radio Access Network). The basic functions of the RRC protocol of LTE are described in 3GPP TR25.813.

[0040] As those skilled in the art will understand, in UMTS, an automatic repeat request (ARQ) function is performed in the RLC layer residing in the radio network controller (RNC). Long Term Evolution (LTE) moves the ARQ function from the RNC to the eNB, where closer interaction can exist between ARQ and HARQ (in the MAC layer and also in the eNB).

[0041] Various issues regarding DRX in LTE-ACTIVE are considered here.

[0042] DRX signaling flow

[0043] A very efficient signaling process for activating and deactivating DRX and specifying the duration of the DRX cycle is required in order to support a large number of UEs in the cell that utilize DRX in the LTE-ACTIVE state.

[0044] As those skilled in the art will understand, during the period when the receiver of the UE is turned off due to the DRX operation, if the evolved Node B (eNB) involved transmits data to the UE, the UE cannot receive the data. Therefore, instructions are needed to ensure that the UE and

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The eNB synchronizes on when to activate and deactivate DRX.

[0045] The indication between the UE and the eNB may be signaled by radio resource control (RRC) or layer 1/layer 2 (L1/L2) explicit signaling. As will be understood, however, explicit signaling is not desired.

[0046] A more effective solution includes optional fields in the MAC header of the MAC-PDU (MAC Protocol Data Unit) to indicate DRX activation and deactivation. This field preferably indicates the DRX value and timing margin used for activation and deactivation. For example, in the preferred embodiment, a value of zero means that DRX in the DRX value field is deactivated. On the contrary, if the data to be transmitted in the next MAC-PDU is the last one in the buffer for the UE, the eNB may extend the MAC header field to include the initial value of the DRX length. For example, this may be 320 milliseconds. The timing margin is explained below, and for the receiving state of the MAC-PDU between the UE and the eNB, the timing margin is used to reduce the misinterpretation of the results of NACK to ACK or ACK to NACK.

[0047] For example, three bits may be added to the MAC header to indicate 8 values of the DRX cycle. Therefore, in addition to sending a specific time value, a bit value from 000 to 111 can indicate one of 8 discrete values.

[0048] In the alternative, a smaller field (eg, 2 bits) can be used in the MAC header to indicate increment or decrement. The RRC can indicate a default value, and if the MAC header indicates increment or decrement, the UE can change to a pre-designated value.

[0049] Once the UE receives the DRX value, the UE acknowledges to the eNB by transmitting HARQ ACK, and starts DRX at the system frame time considering the propagation delay and processing delay at the T eNB. When the eNB receives the ACK from the UE, DRX also starts at the next system frame time. As will be understood, the eNB does not turn off its transceiver, but simply learns not to transmit messages to individual UEs.

[0050] During the DRX cycle, if new data arrives at the eNB, according to the amount of data in the buffer or the required quality of service, the eNB may send a MAC-PDU with a header extension set for DRX deactivation or a shorter DRX length . The UE therefore reconfigures DRX and acknowledges the MAC-PDU. When the eNB receives the ACK, it reconfigures DRX. As mentioned above, the deactivation is done only by setting the length value to zero.

[0051] Reference is now made to Figures 3a and 3b. Figure 3a shows an example method for controlling DRX in the LTE-ACTIVE state. The process starts at step 300 and proceeds to step 310 where data will be transmitted to the UE. Those skilled in the art will understand that data transmission in the LTE-ACTIVE state utilizes the MAC-PDU at the data link layer to transmit data.

[0052] The process then proceeds to step 312, where a check is made to see if the buffer of data to be sent to the UE is empty after the next transmission. If not, the process proceeds to step 310 of transmitting data to the UE. Alternatively, if the buffer will be empty after the next transmission and the data arrival rate is lower than the threshold, the process proceeds to step 314.

[0053] In step 314, the eNB sets DRX activation in the MAC-PDU header. As mentioned above, this includes the DRX activation value indicating the length of the DRX cycle. In another embodiment, the eNB may simply indicate the increase of the DRX interval. The UE reconfigures the existing DRX interval to a reduced predetermined interval. The predetermined interval may be notified by system broadcast or RRC signal, a predetermined interval that is known between the eNB and the UE or signaled in advance from the eNB to the UE via explicit signaling.

[0054] Then the process proceeds to step 316. In step 316, the data including the modified MAC-PDU header is sent to the UE.

[0055] Reference is now made to FIG. 3b. In step 318, the UE receives the data and checks the DRX activation specified in the MAC-PDU header. The process proceeds to step 320. In step 320, the UE sends an acknowledgement (ACK) to the eNB, and starts DRX at the system frame time taking into account the propagation delay and processing delay at the eNB.

[0056] In step 330 of FIG. 3a, the eNB receives the ACK from the UE and starts DRX at the next system frame time.

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[0057] As will be understood, DRX can continue until various events that need to adjust DRX occur. One event is the reception of UE data from the aGW through the eNB. According to the amount of received data, DRX can be deactivated or the cycle of DRX can be reduced. Other events that need to adjust DRX include: the signal power level between the eNB and the UE changes, or the DRX cycle may gradually increase due to continuous data inactivity. These other events are discussed in more detail below.

[0058] In step 332, the eNB checks whether DRX needs to be adjusted. As mentioned above, this may be the case when data to be sent to the UE is received. Here, DRX is deactivated or adjusted periodically.

[0059] According to step 332, if DRX does not need to be adjusted, the process returns to step 332, and continues to check whether DRX needs to be adjusted.

[0060] Once the process in step 332 finds that DRX needs to be adjusted, the process proceeds to step 334 of adjusting DRX. This can deactivate DRX by transmitting DRX zero value or shorter DRX or longer DRX as needed.

[0061] In step 336, the MAC-PDU with the modified header is sent to the UE. The MAC-PDU in step 336 also includes any data that has been received by the eNB and needs to be transmitted to the UE.

[0062] Referring to FIG. 3, the process then proceeds to step 318. In step 318, the MAC-PDU with the modified header is received at the UE. The UE identifies the DRX cycle to be adjusted, and in step 320, the UE sends to the eNB Acknowledge, and adjust its DRX cycle at the same system frame time that considers the propagation delay and processing delay as at the eNB.

[0063] Referring to FIG. 3a, in step 342, the eNB receives the ACK and starts the modified DRX cycle at an appropriate system frame time. Then the process returns to step 332 to check whether DRX needs to be adjusted again.

[0064] Those skilled in the art will understand that one of the above-mentioned problems occurs in the case of ACK or NACK misinterpretation. Specifically, due to poor channel conditions, Hybrid Automatic Repeat Request (HARQ), which is a modification of the ARQ error control method, cannot always correctly demodulate ACK or NACK. Therefore, in some cases, one may be interpreted as another. Since DRX activation and deactivation occur in the MAC-PDU header, it is necessary to deal with the misinterpretation of ACK to NACK or NACK to ACK. [0065] A solution that can solve the above problem is to introduce a timer threshold before activating or deactivating DRX.

[0066] When the UE responds negatively to the MAC-PDU with DRX header information, the UE does not know that it should adjust the DRX cycle. The UE will expect a retransmission from the eNB. If a NACK to ACK misinterpretation occurs, the eNB will receive the ACK and will not send a retransmission, and the DRX cycle will be changed. The UE waits for a period of time to receive the retransmission. If the UE does not receive the expected retransmission, the waiting time should be limited by the upper threshold (HT-A) that takes into account possible ANCK to ACK misinterpretation. If the UE does not receive the retransmission, it should maintain its current DRX state. The eNB will expect to exchange information with the UE in the next DRX cycle. If the UE does not respond, the eNB should revert to the previous DRX cycle and try to "synchronize" with the UE.

[0067] Even when the UE acknowledges the MAC-PDU, the UE needs to wait for retransmission due to possible ACK to NACK misinterpretation or possible ACK to DTX misinterpretation by the eNB. The waiting time should be limited by the upper threshold (TH-B).

[0068] If the UE loses the data indicated on the L1/L2 signaling channel, assuming that the eNB will retransmit at the next earliest opportunity, the UE needs to check the L1/L2 signaling channel for a specific duration (TH-C).

[0069] Based on the above-mentioned various threshold parameters, the shortest time between DRX activations should be greater than (max(TH-A, TH-B)+TH-C)). The threshold can be signaled through system broadcast or RRC signaling.

[0070] Various scenarios are considered here:

[0071] DRX activation and ACK to NACK error:

[0072] Due to ACK to NACK misinterpretation or ACK discontinuous transmission (DTX) misinterpretation (ie, the channel conditions are so bad that the ACK appears to be noise to the receiver), the following occurs. The UE receives the DRX activation in the MAC-PDU header and sends an ACK to the eNB. The eNB receives the ACK, but misinterprets the ACK into NACK or DTX. This causes the UE to be at the eNB

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DRX was activated before, which caused the UE to miss the MAC-PDU retransmission from the eNB.

[0073] In the above case, the UE may wait for a timing margin before activating DRX to resolve ACK to NACK or DTX misinterpretation. The margin can be based on the normal time it takes for retransmissions to occur, and weighted by the average number of HARQ retransmissions experienced to the UE. DRX activation can be indicated through RRC signaling or in the MAC-PDU header extension. When the UE positively responds to the retransmission before the timing margin expires, the UE will start DRXo at the system frame time including the processing time of two consecutive misinterpreted eNBs considering the propagation delay and assuming that there is almost no possibility of two consecutive misinterpretations.

[0074] DRX activation and NACK to ACK error:

[0075] Similarly, if the UE sends a NACK for a MAC-PDU, it may be misinterpreted as an ACK by the eNB. In the case of DRX activation, the eNB activates DRX before the UE. If the eNB maintains CQI resources for the UE within a short period of time after activating DRX, the eNB will detect that the UE has not activated the indicated DRX by checking the frequency of the CQI report , And signal DRX activation through L1/L2 control signaling. If the eNB releases CQI resources and allocates them to other UEs just after activating DRX, the CQI reports from the two UEs will conflict. The eNB can use time division multiple access or code division multiple access to avoid this conflict.

[0076] In the case where the RLC is operating in the Acknowledgement Mode (AM), when a NACK to ACK misinterpretation occurs, the recovery of DRX synchronization between the eNB and the UE is established via a normal RLC retransmission mechanism. This is because the RLC layer in the transmitter will determine that the PDU is lost, and therefore initiate normal ARQ recovery by retransmitting the original data that was not received.

[0077] In the case where the RLC is operating in a negative answer mode (UM mode), there is no recovery mechanism. One solution is that in HARQ, the receiver sends a channel quality indicator (CQI). In continuous reception, the channel quality indicator is repeated every 100 milliseconds, for example. Based on the CQI report, the transmitter determines and indicates the coding rate, modulation scheme, and transport block size. During the activation of DRX, the eNB may expect, for example, one CQL every second. If the eNB obtains the CQI at a different rate (for example, 300 milliseconds), it learns that the UE is not in DRX and correction can occur. For the deactivated DRX in NACK to ACK misinterpretation, the UE still considers it to be in DRX, while the eNB considers it to be in an activated state. This will result in loss of data; however, the indication of DRX deactivation occurs again in the next MAC-PDU.

[0078] Therefore, assuming that the CQI (channel quality indicator) report is aligned with the DRX length, the eNB will learn whether the DRX activation is completed in the UE by checking the frequency of the CQI report. If it is not completed, the eNB can use L1/L2 signaling or just send the MAC-PDU header to correct DRX activation or reconfiguration.

[0079] When the eNB receives a timing advance (TA) request message from a UE that should be in DRX, another recovery method may be triggered. When the UE restores the power of its transceiver and thus assumes the DRX state, the UE will usually need to send control (eg, measurement reports) and other data messages to the eNB. It is important that the UE has the correct TA before sending these messages, so that the UE messages will not partially overlap with messages from other UEs when they arrive at the eNB. Therefore, after the DRX cycle, the UE will usually send a TA request on the random access channel to obtain the correct TA from the eNB. If the TA request arrives at the moment when the UE should be in DRX, the eNB will learn that the UE did not correctly receive the last DRX activation or modification. The eNB can then revert to the previous DRX cycle for the UE and resume DRX cycle synchronization.

[0080] DRX deactivation and ACK to NACK error:

[0081] In the case of DRX deactivation or DRX length reconfiguration, ACK to NACK or DTX misinterpretation causes the UE to deactivate DRX before the eNB. If the UE affirms the normal retransmission from the eNB and the eNB successfully receives ACK, this situation does not require special handling.

[0082] DRX deactivation and NACK to ACK error:

[0083] In the case of DRX deactivation or DRX length reconfiguration, NACK to ACK misinterpretation causes the eNB to communicate with the UE.

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Deactivate DRX before, which can cause the UE to miss new data transmission. A possible solution to this problem is that the eNB instructs DRX to deactivate on the MAC-PDU header of the subsequent MAC-PDU. It is assumed that continuous misinterpretation is extremely unlikely, and DRX reconfiguration is not required when only one MAC-PDU is needed to transmit new data that has arrived at the eNB.

[0084] DRX auto increment

[0085] Another consideration is the incremental expansion of DRX. In a preferred embodiment, during the establishment of a radio bearer (RB), a rule indicating how to increment or decrement the DRX cycle (for example, by a factor of 2) may be signaled. This rule is carried in the RRC RB establishment/reconfiguration or measurement control message for the UE. In this case, if no data is received after N current DRX cycles, the eNB and UE automatically increment the DRX length to the next longer value. This eliminates the need to signal between the eNB and the UE to increase the DRX length, and therefore saves network resources and battery resources.

[0086] UE requests DRX

[0087] Since the UE terminates all protocols from Layer 1 to Layer 7, the UE can determine whether it can enter the longest DRX value after receiving some specific data packets, instead of waiting for the network to gradually increase the DRX value. However, in this case, the UE is required to be able to request DRX activation.

[0088] As those skilled in the art will understand, the eNB is not very smart when considering the higher layer or application behavior of the UE, and therefore will normally increment DRX. However, the UE can learn that the increase does not need to be gradual under certain circumstances and can immediately enter a higher value.

[0089] The eNB also signals whether the UE can request DRX activation via a radio resource control radio bearer establishment or reconfiguration message.

[0090] However, if the UE needs to inform the eNB of the possibility of rapid changes, user plane data is not always available to piggyback the DRX request from the UE. In a preferred embodiment, L1/L2 signaling messages are used. The UE sends a DRX request message to the eNB, and the eNB answers with the DRX grant message.

[0091] In addition to applying data stream characteristics, the UE may also consider various considerations to determine the correct DRX cycle. For example, the movement and location within the cell can be considered. If the UE is moving at a high speed, or if the UE sees a good neighboring cell, the UE can choose to request a shorter DRX cycle to prepare for a possible handover.

[0092] The eNB may also permit a value shorter than the value requested when it learns that the UE is in a high-speed movement state or that the UE has missed the handover opportunity (as described above). The eNB may also consider how close the UE is to the edge of the cell. If the UE is close to the edge of the cell, the eNB may reject or indicate a shorter time value for DRX.

[0093] If allowed by the eNB, the UE indicates the recommended value of the DRX cycle in the optional field of the uplink scheduling request. Even if the UE already has uplink resources, the message can be used if there is no actual resource request part indicated for DRX.

[0094] On the eNB, the eNB responds to the request by indicating the allowable value of DRX. If the DRX request is permitted, the activation time is also indicated.

[0095] In some embodiments, the DRX request can be integrated into the UL scheduling request, and the DRX grant can be integrated into the UL scheduling grant.

[0096] When requesting the DRX value, the UE may also consider its mobility and handover possibility based on the channel quality measurement of the serving cell and its neighboring cells. As described below, the UE can also increase the measurement frequency independently to detect the handover condition more accurately. The UE can consider whether its movement status is high or low based on positioning measurement, accelerometer or L1 data filtering.

[0097] Referring now to FIG. 4a, the process of FIG. 4 starts at step 400 and proceeds to step 410 where the UE receives data.

[0098] The process then proceeds to step 412. In step 412, the UE considers the data and optionally the factors described above.

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Vegetarian. Specifically, the UE may consider the mobility of the UE or the signal strength of neighboring cells.

[0099] Based on the consideration of step 412, the process proceeds to step 414. In step 414, DRX is requested in the L1/L2 uplink scheduling request.

[0100] Reference is now made to FIG. 4b. The process then proceeds to step 416 where the eNB receives the request.

[0101] In step 418, the eNB considers the request and other optional factors as described above. Specifically, the eNB may consider whether the UE has previously missed the cell handover opportunity or is close to the cell boundary, or is moving at a high speed. In step 420, the eNB determines whether to allow the request of step 414 based on the factors in step 418. If so, the process proceeds to step 430, in which it signals that the request has been accepted. If not, the process proceeds from step 420 to step 440, in which the eNB can completely reject the request or suggest a shorter duration of DRX.

[0102] Referring to FIG. 4a, the UE receives a response from the eNB in step 442, and may respond positively in step 444. [0103] As those skilled in the art will understand, long DRX can lead to erroneous handover decision and execution of the UE. When DRX is activated, the receiver will have fewer measurement opportunities, and therefore degrade the accuracy of channel condition estimation. Due to the deterioration of measurement accuracy caused by DRX, the UE missed the handover opportunity.

[0104] Based on the foregoing, if the eNB learns that the UE is located close to the edge of the cell, it may reject the request or permit the shortened DRX value. The decision can be based on the current timing adjustment value (assuming it is available), UE mobility status (no matter high or low), the number of handovers in a specific period considering the cell radius or the number of opportunities for the UE to leave the serving cell, or the actual size of the cell ( Macro, micro, or pico) real understanding. These are all factors that can be considered in step 418 of Figure 4b.

[0105] Measurement accuracy

[0106] The third factor for DRX in the LTE-ACTIVE state is the possibility of missing handover opportunities. Since the UE receiver is turned off during DRX, compared to continuous measurement, the measurement quality of the service and neighboring cells may be degraded. This degradation can lead to premature handovers or missed handover opportunities that should be avoided as much as possible.

[0107] In order to reduce the number of premature handovers or missed handover opportunities in DRX, in a preferred embodiment, when necessary, the UE is allowed to have a measurement period shorter than the DRX period. For example, if the channel quality of the serving cell is lower than the threshold A, the UE can start to continue measurement or a shorter measurement period to prepare possible handover conditions. If the result is a false alarm (ie, if the channel quality obtained by continuous measurement is greater than the threshold B), the UE may return to the measurement period equal to the DRX period. As those skilled in the art will understand, the two thresholds represent better channel conditions than the value that triggers the handover, so that a sufficient level of accuracy is obtained when the handover condition needs to be evaluated, so that missed handover opportunities can be reduced.

[0108] In an embodiment of the present disclosure, the measurement interval may be configured to be equal to the DRX interval divided by N, where N is an integer. This will be a situation where the mobile phone is expecting to switch and/or there is high-speed movement.

[0109] The network can configure the threshold and a shorter measurement period, and signal the UE via broadcast information or RRC measurement control messages. Once the UE has shortened the measurement period, the MAC-PDU header can indicate the shortened DRX period value to the network. [0110] The above example is when there is an RRC connection or a radio bearer is established. In this case, the eNB can indicate the two channel quality values of the shorter DRX start and stop respectively, and the ratio of the measurement to the DRX cycle.

[0111] On the UE, according to the channel quality measurement compared with the threshold, the UE acts on the RRC signaling and starts or stops a shorter measurement period.

[0112] Refer to FIG. 5. Figure 5 shows the various areas where the UE is located, including thresholds to indicate the DRX cycle. In the first area 510, the DRX cycle is equal to the measurement cycle. The UE stays in this area until it reaches the threshold 520 where it needs to start a shorter measurement period.

[0113] Until the signal degrades to indicate the handover condition 530 or if the signal increases until the UE reaches the indicated DRX cycle

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If the upper threshold 540 is equal to the measurement period, the UE continues to have a shorter measurement period.

[0114] Preferably, the eNB signals the following information during radio bearer establishment or measurement control messages:

[0115] A higher threshold used to extend the DRX cycle. The higher threshold indicates higher channel quality and/or signal strength;

[0116] A lower threshold used to shorten the DRX cycle. The lower threshold indicates lower channel quality and/or signal strength;

[0117] The trigger time associated with the higher threshold and the lower threshold; and

[0118] Instructs the handover conditions for continuing the measurement, such as "the best cell changed" and the measurement period is equal to zero.

[0119] The diagram of FIG. 7 shows an example in which in the absence of uplink (UL) data, the channel quality or signal power starts below a lower threshold (LTV), and then exceeds a higher threshold (HTV) ) Ο In this case, a shortened measurement period is achieved between A and B, and the DRX period is equal to the measurement period before A and after B.

[0120] FIG. 8 shows an example in which in the presence of uplink (UL) data, the channel quality or signal power starts below the lower threshold (LTV) and then exceeds the higher threshold (HTV). In this case, if the channel quality is below the lower threshold for more than a certain duration (time to trigger), the UE shifts to a short measurement period. If there is uplink data, the UE starts the initial UL access procedure to obtain UL resource grant by sending a scheduling request. The scheduling request or the header of the uplink MAC-PDU can indicate a shorter DRX cycle request. The eNB can respond to the request by sending a scheduling grant message with the preferred DRX value, or the eNB can indicate the preferred DRX value in the downlink MAC-PDU. When receiving the scheduling grant or acknowledging the downlink MAC-PDU, the eNB can start with the new DRX value. Then the figure shows the channel quality or signal power (as shown in the measurement report) for a specific duration (time to trigger) that exceeds the higher threshold. If UL data is available, the UE indicates in the scheduling request or the header of the MAC-PDU Request for a longer DRX value. The eNB responds to the request by sending a grant message with a preferred DRX value and an indication to start the automatic mode, or the eNB can indicate a preferred DRX value with an indication to start the automatic mode in the header of the next downlink MAC-PDU. When the scheduling permission is received or the downlink MAC-PDU is acknowledged, the automatic mode starts with the initial DRX value specified by the eNB. If the data is not available, the UE needs to send an L1/L2 control message to request automatic DRX increment.

[0121] The example of FIG. 9 shows a switching condition trigger. In this case, the signal gradually degrades until it is below the lower threshold for a certain trigger time, at which point the UE starts to use a shorter measurement. Then the UE looks at the specific duration of the handover condition (trigger time). At this time, the UE initiates the UL access process and transmits a scheduling request in order to obtain the UL resource of the measurement report message. A request to return to the continued reception mode or a zero value DRX can be indicated in the scheduling request or the MAC-PDU carrying the measurement report message_O The eNB responds to the request by sending a scheduling grant message with the preferred DRX value of zero, or the eNB can indicate the preferred DRX value of zero in the next downlink MAC-PDU. When receiving a scheduling permission or an affirmative response to the downlink MAC-PDU, both sides deactivate DRX. Regarding handover, the UE receives the handover command and acquires the downlink synchronization of the target cell. Then the UE indicates the channel quality and/or the signal strength of the target cell in the handover completion response. The eNB can then evaluate when it is safe to activate DRX. If it is safe, the eNB indicates DRX activation in the downlink (DL) MAC-PDU header or L1/L2 control signaling.

[0122] In the above paragraph, the UE requests a shorter or longer DRX cycle, or the DRX value itself is in the scheduling request or the header of the uplink MAC header. The eNB responds to the UE by specifying a preferred DRX cycle with an indication of whether the automatic DRX increase/decrease principle can be applied in the scheduling grant or the downlink MAC-PDU header.

[0123] In another embodiment, the scheduling request indicates the reason for uplink access. For example, suppose a VOIP call is initiated during the 2.56 second DRX cycle. In order for the network to respond quickly to the VOIP call establishment, the UE sends an uplink access

The reason for the dispatch request (for example, call establishment). The eNB replies to the request by sending a scheduling grant indicating a DRX value of zero (preferred DRX value).

[0124] Detection and processing of very late handover

[0125] In order to utilize DRX in the LTE_ACTIVE state, it is preferable for the UE to determine whether a standardized criterion for a handover opportunity is missed. If such conditions are met, the UE should establish a connection with the neighboring cell instead of the serving cell. As those skilled in the art will understand, in the LTE infrastructure, only a network-based handover process is applied, and there is no UE-based process, such as cell reselection used in UMTS.

[0126] In a preferred embodiment, if the channel quality of the serving cell is smaller than the channel quality of the neighboring cell by the threshold C for a certain duration T, the UE needs to connect itself to the neighboring cell on the target eNB. The values C and T can be signaled through system broadcast information or RCC signaling.

[0127] The process of switching to the target eNB includes the following steps:

[0128] 1. Start the UL initial access procedure to obtain the timing advance value of the target cell and the uplink resources for subsequent control messages;

[0129] 2. Transmit a reconnection request with current RNTI (Radio Network Temporary Identifier) and previous cell ID to the target eNB;

[0130] 3. The target eNB connects to the serving eNB in order to obtain the UE context and downlink data that needs to be transmitted. The target eNB also connects itself to the access gateway and removes the serving eNB from the aGW; and

4. The target eNB transmits a reconnection response with a new RNTI and uplink grant to the UE.

[0132] Optional components include status messages to be carried through reconnection requests and responses, so that the amount of data transferred between the target eNB and the serving eNB and between the target eNB and the air interface of the serving eNB and the UE can be minimized .

[0133] The optimization includes the reconnection request to be sent together with the status report showing the PDCP (Packet Data Convergence Protocol) SUD (Server Data Unit) sequence number successfully received by the UE in step 2 above. This information helps reduce the amount of downlink user data to be transmitted over the air from the serving eNB to the target eNB and to the UE. Since the RLC may be reset during the process, the PDCP SDU sequence number is required.

[0134] Similarly, the reconnection response can be sent together with a status report showing the PDCPSDU sequence number successfully received by the serving eNB, so that the UE can retransmit the missing data.

[0135] In addition, if the target eNB finds that there is no data to be transmitted from the serving eNB and aGW, a reconnection instruction

DRX is activated.

[0136] The above is shown in FIG. 6a, where, in step 612, the UE obtains the timing advance value for the target cell and the uplink resources for subsequent control messages. Then the process proceeds to step 614. In step 614, the UE transmits a reconnection request with the current RNTI and cell ID to the target eNB. Then in step 650, the UE waits and acknowledges the response from the target eNB.

[0137] Referring to FIG. 6b, in step 615, the target eNB receives the request and then proceeds to step 616. In step 616, the target eNB contacts the serving eNB in order to obtain the UE context.

[0138] In step 618, in step 615, the target eNB transmits a reconnection response with a new RNTI and uplink grant to the UE.

[0139] The above can be implemented on any UE. Such UEs include, but are not limited to, personal digital assistants, cellular phones, wireless data devices, and so on.

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[0140] The embodiments described here are structures, systems, or methods having elements corresponding to the elements of the technology of the present application. This written description may enable those skilled in the art to make and use embodiments with optional elements that also correspond to the elements of the technology of the present application. Therefore, the expected scope of the technology of the present application includes other structures, systems, or methods that are the same as the technology of the present application described herein, and also includes other structures, systems, or methods that are not substantially different from the technology of the present application described herein.

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